Rafael Nadal called for greater understanding from umpires after once again falling foul of the time violation rules.

Players are not supposed to take more than 20 seconds between points at grand slams but Nadal, with his many ticks and foibles, often strays outside that limit.

Umpires began cracking down on abuses last season and Nadal has been warned repeatedly.

It happened again during his fourth-round clash with Kei Nishikori at the Australian Open on Monday, most notably at a crucial stage of the third set.

With Nadal serving at 4-4 and deuce, he was warned by umpire Eva Asderaki for a second time and briefly lost his cool.

He dropped his serve but broke Nishikori back straight away and went on to win the match 7-6 (7/3) 7-5 7-6 (7/3).

Nadal said: "The negative thing in my opinion is not the warning. The negative thing is the moment. You can choose another moment to do it, not that one.

"Another thing is she didn't advise me before the second warning that I was still going slow.

"We need referees who understand the game. The rules cannot go against the good show.

"I accept the rules. Sometimes I am wrong. Sometimes I am too slow and I accept that. I'm going to try to go quicker for the future."

Every set lasted more than an hour, with Nadal having to show off his legendary battling qualities rather than the sublime form he demonstrated in crushing Gael Monfils on Saturday night.

It was a troublesome afternoon for the world number one, who needed treatment for a large blister on his hand and broke a shoelace in taking a tumble, requiring a trip off court for a new pair of shoes.

He said: "The feeling was not the same (as the Monfils match). It was a little bit worse, my feeling.

"He was able to play more inside the court. I think I played a little bit too short. The other day I was able to hit longer and to take advantage with my shots.

"But the victory of today has much more value than the victory of two days ago. Because when you are playing that good, the normal thing is to win.

"I think the concentration for me was okay the whole match. I played very focused, fighting for every ball.

"Kei played a fantastic match, just a few mistakes in some moments that were tough ones. But for the rest he played very aggressive, he went for his shots.

"He came on court with determination to take the ball very early and go for winners. He really had the right feelings to do it. It was a tough match, a very important win. I'm very happy."

In the quarter-finals, Nadal will face Grigor Dimitrov, who continued to blossom at his breakthrough grand slam with a 6-3 3-6 6-2 6-4 victory over Spain's Roberto Bautista Agut.

The Bulgarian, who has made it further in the tournament than girlfriend Maria Sharapova, said: "I'm really happy to be out there in the quarter-finals but I'm not even close to satisfaction.

"I've been working really hard in the past year, especially in the off-season, so it's nice to see that result.

"I'm really looking forward to the match. I just want to put myself into a good position to play matches like that more often. So that's what I'm working for."

Nadal has won all their three previous matches but each of them has been close.

"I had tough battles with him in the past," said Dimitrov. "There were always little things missing. But I'm quite happy with the way I'm performing so far, so I like my chances."